tail -F log_file | xrootconsole
where -F is a shortcut for --follow=name --retry

You can also use conky, with the variable
tail logfile lines (next_check) in .conkyrc. From the manpage:

Displays last N lines of supplied text file. The file is checked every 'next_check' update. If next_check is not supplied, Conky defaults to 2. Max of 30 lines can be displayed, or until the text buffer is filled.

Note that if you are using linux, tail -f actually waits for the kernel to notify that the file^Wdescriptor has been modified. Not sure about tail -F, but conky is a bit overbloat if you don't need anything else than reading a log file.